if a limit exists in the ordinary sense (not in the sense of the upper limit) then \(\Delta \)  is called the density. Note that it is proved in Lemma 1
[1]} that
\(\lim \limits _{r\rightarrow \infty } r(t)/t^{\rho _{1}+\varepsilon }\rightarrow 0,\,\varepsilon >0.\) 
